334 PHILOSOPHICAL TRANSACTIONS. LaNNO 1686. 



weaker in the quadratures : and from hence this difference should be still more 

 and more considerable, as the port is farther removed from the sea. 



A Demonstration of the Felocitt/ with which the Air rushes into an exhausted 

 Receiver. By Dr. D. Papin, Reg. Soc. S. N° 184, p. 193. 

 ' There being several occasions wherein it would be useful to know the velocity 

 of the air, according to the several pressures that may urge it, the Royal 

 Academy at Paris has attempted it by experiment, viz. by means of a bladder, 

 sometimes filled up with water, and sometimes with air, they found that, although 

 the weight to squeeze out these fluids, and the hole to discharge them were the 

 same, yet the bladder, when full of air, could be emptied in the 25th part of 

 the time that was required for emptying the water; whence they concluded, that 

 the velocity of the air is 25 times greater than that of water, when both fluids 

 suffer the same pressure. This experiment was very ingenious, but not quite 

 perfect. For the air yields much, and so the bladder, filled with it, will be- 

 come pretty flat as soon as a considerable weight is laid upon it. It is plain 

 therefore, that the weight, bearing on a large surface does not press every part 

 with the same force, as it would do if the bladder did for a while remain dis- 

 tended, as it does when full of water ; besides, the water itself, being heavy in 

 the bladder, makes some pressure : so that it appears, that the pressure in this 

 experiment was not quite so great upon the air as on the water. I have there- 

 fore thought of another way, which I think better, founded on this hydrostati- 

 cal principle, that liquors have a power to ascend as high as their source, and 

 although the resistance of the medium always hinders jets d'eau, in the open 

 air, from reaching quite so high, yet the liquor at its first spouting out, has the 

 necessary velocity to carry it to that height. 



Prop. 1. — From this principle may easily be deduced this proposition, viz. 

 that of two different liquors, urged by the same pressure, that which is specifi- 

 cally lighter must ascend higher than that which is heavier, and their heights 

 will be reciprocally in the same ratio as their specific gravities. Thus quicksilver 

 being 134- times heavier than water, bears as much pressure when its spring is 

 one foot above the hole, as water does when it is 134^ feet high, and the height 

 to which mercury shall ascend, will be 13^ times less than the height to which 

 water shall be driven by those equal pressures. 



^,wj Projb. 2. — From the foregoing proposition another may easily be deduced, 

 viz. that of difi'erent liquors under the same pressure, those specifically lighter 

 must acquire a greater celerity, and their different velocities be to one another, 

 as the roots of the specific gravities of the said liquors. For, by prop. 1, the 

 , heights to be attained, are reciprocally in the same ratio as the specific gravi- 

 ties : now Galileo, Huygens, and others have demonstrated, that the velocities 



